Light-emitting material and light-emitting element

ABSTRACT

A light-emitting material includes a matrix section  12  and light-emitting sections  11  dispersed and buried in the matrix section. The matrix section  12  comprises a first material and the light-emitting sections comprise a second material showing a eutectic relationship with the first material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a light-emitting material containing anano-phosphor, a light-emitting element using the same and a method ofmanufacturing the same.

2. Related Background Art

Flat panel displays (FPD) realized by using phosphor thin films andphosphor powders having a light-emitting effect have been and areattracting attention. Flat panel displays include plasma displays (PDP),field emission displays (FED) and, electro-luminescent displays (ELD).Such phosphors that are used for displays of a specific type arerequired to match the characteristic features of the displays.

Phosphors that have been prepared are conventionally produced by addingone or more than one transition metals and/or one or more than one rareearth elements as luminescent center to oxides or sulfides as matrix.Examples of known phosphors for inorganic EL include ZnS:Mn, SrS:Ce,Eu,CaS:Eu, ZnS:Tb,F, CaS:Ce, SrS:Ce, CaGa₂S₄:Ce, BaAl₂S₄:Eu, Ga₃O₃:Eu,Y₂O₃:Eu, Zn₂SiO₄:Mn and ZnGa₂O₄:Mn. Examples of other phosphors thathave been prepared include Y₂O₂S:Eu³⁺, Gd₂O₂S:Eu³⁺, YVO₄:Eu³⁺,Y₂O₂S:Eu,Sm, SrTiO₃:Pr, BaSi₂Al₂O₈:Eu²⁺, BaMg₂Al₁₆O₂₇:Eu²⁺,Y_(0.65)Gd_(0.35)BO₃:Eu³⁺, La₂O₂S:Eu³⁺,Sm, Ba₂SiO₄:Eu²⁺,Zn(Ga,Al)₂O₄:Mn, Y₃(Al,Ga)₅O₁₂:Tb, Y₂SiO₅:Tb, ZnS:Cu, Zn₂SiO₄:Mn,BaAl₂Si₂O₈:Eu²⁺, BaMgAl₁₄O₂₃:Eu²⁺, Y₂SiO₅:Ce and ZnGa₂O₄:Mn.

Inorganic EL displays are among the displays that are attractingattention because polycrystalline inorganic phosphors can be used forthem to provide a large display area with relative ease and they show anenhanced durability in the operating environment. Efforts for developingfull color EL displays that utilize in organic EL have been paid inrecent years although no highly efficient phosphor showing a high degreeof color purity and a high luminance level has so far been obtained.Therefore, it is indispensable to develop a high performance phosphor inorder to realize a full color inorganic EL display.

Meanwhile, the light-emitting characteristics of very small particles ofsemiconductors such as Si, Ge and II-VI compounds having a diameter notgreater than tens of several nanometers that are attributable to thequantum size effect have been made clear in recent years. The quantumsize effect is believed to be derived from the fact that very fineparticles of semiconductors with nano-crystal structure have a band gapgreater than that of bulk semiconductors. As a remarkable example, ithas been observed that light emitted from CdSe semiconductor fineparticles tends to show a shorter wavelength as the particle diameter isreduced. Additionally, light emitted from semiconductor fine particlesshows a high luminance level because their light-emitting life is veryshort and not longer than 10 ns and light is absorbed and radiated in avery short period of time.

Very fine particles of semiconductors as described above can be producedin an aqueous solution (Journal of Physical Chemistry, B, Vol. 102, p.8,360 (1998)). A technique for fixing very fine particles of asemiconductor generated in an aqueous solution to a solid matrix of apolymer has been proposed (Advanced Material, vol. 12, p. 1,103 (2000)).However, since polymers are poorly resistant to light and heat, the veryfine particles fixed to polymers may easily become degraded.

SUMMARY OF THE INVENTION

In view of the above-identified technological background, it istherefore an object of the present invention to provide a novellight-emitting material.

According to the invention, the above object is achieved by providing alight-emitting material including: a matrix section and light-emittingsections dispersed and buried in the matrix section; the matrix sectioncomprising a first material, the light-emitting sections comprising asecond material showing a eutectic relationship with the first material.

Preferably, said light-emitting sections are granular or cylindrical andhave pointed apexes.

In another aspect of the present invention, there is provided alight-emitting element comprising: a light-emitting layer and a pair ofelectrodes arranged so as to sandwich the light-emitting layer; thelight-emitting layer including a matrix section and light-emittingsections dispersed and buried in the matrix section; the matrix sectioncomprising a first material, the light-emitting sections comprising asecond material showing a eutectic relationship with the first material.

In still another aspect of the invention, there is provided a structurecomprising a base body including light-emitting sections adapted to emitlight in response to a voltage applied thereto and comprising at leastone of two or more than two materials constituting a eutecticcomposition and a second section comprising a material or materials ofthe eutectic composition other than the material or materials of thelight-emitting sections, said light-emitting sections having a profileadapted to give rise to a quantum effect attributable to confinedmovements of electrons.

In still another aspect of the invention, there is provided alight-emitting material of a eutectic composition, at least one of theconstituent materials of the eutectic composition forming light-emittingsections, the light-emitting sections being in the form of fineparticles surrounded by the remaining material or materials of theeutectic composition.

There is also provided a light-emitting material of a eutectic material,at least one of the constituent materials of the eutectic compositionforming light-emitting sections, the light-emitting sections being inthe form of cylinders surrounded by the remaining material or materialsof the eutectic composition. The ends of the cylinders of thelight-emitting sections may have pointed apexes or may be narrowed.

Preferably, the size of each light-emitting section is not greater than1 μm. Preferably, a light-emitting material according to the inventionis in the form of a thin film. Preferably, a light-emitting materialaccording to the invention comprises oxides. When a light-emittingmaterial according to the invention comprises oxides, variouscombinations of oxides can be used for the purpose of the invention.Examples of combinations of oxides include (1) magnesium oxide and anoxide of a rare earth element, (2) nickel oxide and an oxide of a rareearth element, (3) vanadium oxide and a vanadium composite oxidecontaining a rare earth element, (4) silicon oxide and a siliconcomposite oxide containing a rare earth element and (5) tungsten oxideor zinc oxide and a tungsten composite oxide containing zinc.

More preferably, a light-emitting material according to the invention isin the form of a thin film with a thickness not greater than 5 μm andthe size of each light-emitting section thereof is not greater than 100nm.

In still another aspect of the present invention, there is provided alight-emitting element formed by using the light-emitting materialdescribed above, which may be an inorganic EL element.

In still another aspect of the present invention, there are provided animage display apparatus, an illumination apparatus and a printingapparatus comprising the light-emitting element described above.

In still another aspect of the present invention, there is provided amethod of manufacturing the light-emitting material.

In a further aspect of the invention, there is provided a method ofmanufacturing a light-emitting material by forming a film of thelight-emitting material on a substrate, said method comprising a step offorming a film of a eutectic material typically by sputtering, at leastone of the constituent materials of the eutectic composition forminglight-emitting sections, the light-emitting sections being in the formof fine particles surrounded by the remaining material or materials ofthe eutectic composition. Preferably, the temperature of the substrateis not lower than 400° C. during the film forming process.

There is also provided a method of manufacturing a light-emittingmaterial by forming a film of the light-emitting material on asubstrate, said method comprising a step of forming a film of a eutecticmaterial typically by sputtering, at least one of the constituentmaterials of the eutectic composition forming light-emitting sections,the light-emitting sections being in the form of cylinders surrounded bythe remaining material or materials of the eutectic composition.Preferably, the temperature of the substrate is not lower than 400° C.during the film forming process.

Thus, according to the invention, it is possible to provide a novellight-emitting material. Since light-emitting sections in the form offine particles or cylinders are dispersed in a matrix section, thelight-emitting efficiency is much improved if compared with alight-emitting material where light-emitting sections are held in closevicinity or agglomerated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic illustrations of a light-emitting materialaccording to the invention and having light-emitting sections thatappear to be so many fine particles;

FIGS. 2A and 2B are schematic illustrations of a light-emitting materialaccording to the invention and having light-emitting sections thatappear to be so many cylinders;

FIGS. 3A, 3B and 3C are schematic illustrations of a speciallight-emitting material according to the invention;

FIGS. 4A and 4B are schematic cross sectional views of light-emittingelements according to the invention;

FIGS. 5A and 5B are schematic cross sectional views of otherlight-emitting elements according to the invention;

FIG. 6 is a schematic cross sectional view of a phosphor thin filmaccording to the invention;

FIG. 7 is a schematic perspective view of a light-emitting materialhaving pointed apexes; and

FIG. 8 is a schematic cross sectional view of a light-emitting elementfor acquiring EL, illustrating the structure thereof.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, the present invention will be described by referring to theaccompanying drawings that illustrate preferred embodiments oflight-emitting material according to the invention.

For the purpose of the present invention, the expression that the firstmaterial and the second material show a eutectic relationship refers tothat the two materials have a relationship where crystal A (of the firstmaterial) and crystal B (of the second material) will solidifysimultaneously at a given temperature in a phase diagram of the twomaterials.

For the purpose of the present invention, the expression of a eutecticcomposition refers not to the composition of the component elements of acorresponding eutectic material but to the composition of the compoundsor the alloys of each region separately formed by a eutectic effect in aeutectic material. Additionally, the expression of the size oflight-emitting sections refers to the average of the diameters of thelight-emitting sections buried in a matrix if the light-emittingsections are formed by fine particles. The expression of the size oflight-emitting sections also refers to the average of the diameters ofthe light-emitting sections buried in a matrix if the light-emittingsections are formed by cylindrical pieces.

FIGS. 1A, 1B, 2A, 2B and 3A through 3C schematically illustrate examplesof thin film light-emitting materials.

FIGS. 1A and 1B illustrate a light-emitting material havinglight-emitting sections that appear to be so may fine particles andFIGS. 2A and 2B illustrate a light-emitting material havinglight-emitting sections that appear to be so many cylinders. FIGS. 3Athrough 3C illustrate a special light-emitting material havinglight-emitting sections only in part of the thin film of thelight-emitting material. In the drawings, 11 denotes a light-emittingsection that appears to be a fine particle and 21 denotes alight-emitting section that appears to be a cylinder, whereas 12 and 22refer to a matrix section and 31 refers to a thin film light-emittingsection.

FIG. 1A is a schematic cross sectional view of a thin film of thelight-emitting material in which phosphor sections appear to be so manyfine particles and FIG. 1B is a schematic plan view of the thin film. Ifthe eutectic materials are compound A and compound B, the light-emittingsections 11 that appear to be so many fine particles are formed by thecompound A, whereas the matrix section 12 is formed by the compound B.While the optimal size of the light-emitting sections depends on thetype of the compound A and the configuration of the element realized byapplying the thin film, it is preferably not greater than 1 μm, morepreferably not smaller than 0.5 nm and not greater than 100 nm. Whilethe volume density of the fine particles is not particularly limited,the overall specific volume density is preferably not lower than 10% andnot higher than 70% because the light-emitting efficiency is reducedwhen fine particles are distributed too sparsely. The fine particles maybe dispersed randomly or regularly.

FIG. 2A is a schematic cross sectional view of a thin film of thelight-emitting material in which phosphor sections appear to be so manyfine cylinders and FIG. 2B is a schematic plan view of the thin film.While the cylinders show a substantially cylindrical profile, they maybe slightly bent or discontinued at a middle part as shown in FIG. 2A.While the optimal diameter of the cylinders depends on the types of thecompounds and the configuration of the element realized by applying thethin film, it is preferably not greater than 1 μm, more preferably notsmaller than 0.5 nm and not greater than 100 nm. While the volumedensity of the cylinders is not particularly limited, the overallspecific volume density is preferably not lower than 10% and not higherthan 70% because the light-emitting efficiency is reduced when cylindersare distributed too sparsely. The cylinders may be dispersed randomly orregularly.

FIG. 7 is a schematic perspective view of a light-emitting material inwhich light-emitting sections are tapered at the opposite ends thereofor have pointed apexes.

FIGS. 3A through 3C are schematic illustrations of other examples ofprofile of a light-emitting material according to the invention. WhileFIG. 3A shows light-emitting sections that appear to be so many fineparticles as in the case of FIGS. 1A and 1B. However, regions free fromlight-emitting sections are intentionally formed in FIG. 3A. When it isdesired to produce a large effect of accelerating electrons near theinterfaces of the electrodes in an inorganic EL element, there areoccasions in which it is desirable to produce regions that are free fromlight-emitting sections. FIG. 3B shows light-emitting sections thatappear to be so many cylinders as in the case of FIGS. 2A and 2B.However, regions free from light-emitting sections are formed at theboth ends of the cylinder in FIG. 3B. Finally, FIG. 3C showslight-emitting sections that appear to be so many fine particles as inthe case of FIGS. 1A and 1B. However, there are one or more than onelight-emitting sections that appear like thin films. As a light-emittingelement, this configuration is preferable in some cases.

When a light-emitting material according to the invention is prepared bymeans of a sputtering process, a structure where light-emitting sectionsare dispersed in a matrix section can be obtained by controlling thesubstrate temperature, the film growth rate, the bias voltage applied tothe deposition substrate and the gas pressure in the deposition chamber.

To obtain a structure where light-emitting sections are dispersed in amatrix section according to the invention, the volume ratio of the firstmaterial (matrix section) and the second material (light-emittingsections) is controlled by changing the content ratio of the componentmaterials of the target. As for the volume rate, the volume of thelight-emitting sections is not lower than 10% and not higher than 70%,preferably not lower 30% and not higher than 60%.

When a sputtering process is used, light-emitting sections are notsometimes dispersed in a matrix section and both the first material andthe second material may come to appear to be fine particles withoutbecoming a film as a result of agglomeration of fine particles,depending on the film-forming conditions.

In such a case, a structure where light-emitting sections are dispersedin a matrix section can be obtained by raising the substrate temperatureand, at the same time, changing the content ratio of the components ofthe target that contains the first material and the second material (forexample, reducing the content of the second material from the target).

When a structure where light-emitting sections are dispersed in a matrixsection is obtained and appear to be as so many particles and it isdesired to change the light-emitting sections to make them appear to beso many cylinders, it is advisable to reduce the growth rate and/orreduce the gas pressure and/or apply a bias voltage to the substrate.

FIGS. 4A and 4B and FIGS. 5A and 5B are schematic cross sectional viewsof light-emitting elements according to the invention, where alight-emitting material according to the invention is used for inorganicEL elements. In the figures, 41 denotes a transparent electricallyconductive film and 42 and 44 denote a dielectric film, while 43 denotesa phosphor film made of a light-emitting material according to theinvention and 45 and 46 respectively denote an electrode film and asubstrate.

FIG. 4A is a conceptual illustration of an AC-driven inorganic ELelement of the type adapted to take out light from the side opposite tothe substrate and FIG. 4B is a conceptual illustration of an AC-driveninorganic EL element of the type adapted to take out light from the sideof the substrate. FIG. 5A is a conceptual illustration of an AC-driveninorganic EL elements similar to that of FIG. 4A but having only asingle dielectric layer. FIG. 5B is a conceptual illustration of aDC-driven inorganic EL element.

A thin film typically made of BaTiO₃ can effectively be used as adielectric film of an AC-driven inorganic EL element. The film thicknessof the dielectric film is preferably between 10 nm and 100 μm. Either ametal thin film or a semiconductor thin film can effectively be used asan electrode of a DC-driven inorganic EL element.

When light is taken out from the side of the substrate as in the case ofFIG. 4B, the substrate 46 is preferably made of transparent glass orplastic so that it may transmit emitted light. Any type of the substratemay be used when light is taken out from the top surface. Then, glass,plastic or ceramic can be used as the material of the substrate,although the use of non-alkaline glass or ceramic is preferable when thesubstrate has to be heated.

An electrode layer needs to be provided when a light-emitting elementaccording to the invention is used as an inorganic EL element foremission of light. Materials that can be used for the electrode layerinclude various metals such as Au, Pt and Ag, alloys and transparentelectrically conductive films. Any appropriate process selected fromvapor phase reaction methods such as the evaporation method, liquidphase reaction methods such as the plating method and solid phasemethods such as the sol-gel method may be used to form the electrodelayer. When an optically functional thin film according to the inventionis used for a light-emitting device that is adapted to take out lightfrom the side of the substrate, it is preferably an electricallyconductive transparent thin film typically made of In₂O₃, SnO₂, ZnO orITO and doped so as to transmit emitted light. In the case where lightis taken out from the top surface, materials primarily consisting ofmetals, alloys and the like are used.

FIG. 6 schematically illustrates a light-emitting element according tothe invention where a light-emitting material according to the inventionis used as phosphor for exciting electron beams. In FIG. 6, 61 denotesan electrode film that is typically made of aluminum and referred to asmetal back. It takes a role of preventing charge-ups and reflectinglight from the phosphor. In FIG. 6, 62 denotes a phosphor film made of alight-emitting material according to the invention, and 63 denotes atransparent electrically conductive film, while 64 denotes a transparentsubstrate typically made of glass.

When a light-emitting material according to the invention is used asphosphor for exciting electron beams, it is preferably slightlyelectrically conductive. Then, it is possible to reduce the thickness ofor omit the electrode film 61. As a result, incident electron beams caneffectively strike the phosphor film.

Now, a light-emitting material according to the invention will bediscussed in greater detail below.

Eutectic refers to a substance in which both crystal A and crystal Bsolidify simultaneously at a given temperature. The temperature isreferred to as eutectic temperature and the overall composition isreferred to as eutectic composition. The point where eutectic appears ona phase diagram is referred to as eutectic point. A phase diagram wherea eutectic point appears is frequently found in two-element systems andalso in oxide systems. For example, the MgO—Y₂O₃ system and the NiO—Y₂O₃system produce eutectic phase. In those systems, however, MgO or Y₂O₃and NiO and Y₂O₃ exist separately at low temperatures. When such asystem is doped slightly with Eu³⁺, the Y part in the Y₂O₃ issubstituted to form red light-emitting sections Y₂O₃:Eu. For example,when the volume ratio of MgO to Y₂O₃:Eu is made equal to about 70% and afilm of the eutectic phase is formed by sputtering, fine particles orcylinders of Y₂O₃:Eu are formed in MgO in a dispersed state.

Beside the above material, V₂O₅ and YVO₄ form a eutectic phase in aV₂O₅—Y₂O₃ system and SiO₂ and EuSiO₃ or EuSiO₃ and Eu₂SiO₄ form aeutectic phase in an EuO—SiO₂ system, whereas WO₃ and ZnWO₄ or ZnWO₄ andZnO form a eutectic phase in a ZnO—WO₃ system. YVO₄ to which a rareearth element is added forms light-emitting sections in a V₂O₅—Y₂O₃system, while both EuSiO₃ and Eu₂SiO₄ form light-emitting sections in aEuO—SiO₂ system.

When a light-emitting material according to the invention is used for aninorganic EL element, the parts of the light-emitting materials arepreferably highly insulating and show a low dielectric constant in manycases.

According to the invention, the first and second materials that show aeutectic relationship are both oxides. Combinations of oxides that canbe used for the purpose of the present invention include magnesium oxideand an oxide of a rare earth element, nickel oxide and an oxide of arare earth element, vanadium oxide and a vanadium composite oxidecontaining a rare earth element, silicon oxide and a silicon compositeoxide containing a rare earth element and tungsten oxide or zinc oxideand a tungsten composite oxide containing zinc.

A light-emitting material according to the invention is adapted toproduce a phosphor thin film that contains highly densely light-emittingsections so that it can suitably be used for phosphor thin films ofinorganic ELs and FEDs.

Now, the present invention will be described further by way of examples.

EXAMPLE 1

An embodiment of light-emitting material according to the invention willalso be described here by referring to FIGS. 1A, 1B and 4A.

A quartz substrate is used as substrate in this example. An electrodefilm 45 is formed by depositing Ti and Au to respective thicknesses of10 nm and 50 nm on a substrate 46 by magnetron sputtering. Subsequently,a dielectric film 44 is formed by depositing BaTiO₃ to a thickness of 2μm also by magnetron sputtering. Thereafter, a phosphor film 43 isformed in a manner as described below.

A target with a composition showing a volume ratio of MgO to Y₂O₃:Euequal to 2 to 1 is prepared. A phosphor film 43 of MgO+Y₂O₃:Eu is formedto a thickness of 5 μm by magnetron sputtering, using the target. Thesubstrate temperature is varied from the room temperature to 1,000° C.during the sputtering process. Then, a dielectric film 42 of BaTiO₃ isformed to a thickness of 2 μm and subsequently a transparentelectrically conductive film 41 of ITO is formed to a thickness of 300nm.

When the obtained film is observed through an electron microscope, it isfound that fine particles of Y₂O₃:Eu are formed in a dispersed state soas to be surrounded by a region of MgO. The average diameter of the fineparticles of Y₂O₃:Eu is between several nanometers and hundreds ofseveral nanometers, although it depends on the film depositionconditions and the crystal is large and clear when the substratetemperature is high in the film deposition process.

When an AC voltage of 1 KHz is applied between the transparent electrodefilm 41 and the electrode film 45 so as to gradually raise the voltage,emission of red light begins when the voltage gets to 150V. The emittedlight is particularly bright when the substrate temperature is not lowerthan 400° C.

In a nano-structure whose size is characteristically not greater thantens of several nanometers, movements of electrons are confined by thequantum size effect that is attributable to the very small particlediameter. Therefore, the light-emitting performance of a light-emittingmaterial according to the invention is improved when very fine particlesof phosphor are used.

EXAMPLE 2

A light-emitting material of an SiO₂—EuO system is prepared in thisexample by using a technique similar to the one used in Example 1.

A p-type Si substrate is used as substrate 46 in this example. Aninsulating film is formed to a thickness of 10 nm on the substrate 46 bymagnetron sputtering. Subsequently, a phosphor film 43 is formed bymagnetron sputtering in a manner as described below.

A target with a composition showing a volume ratio of SiO₂ to EuO equalto 4 to 1 is prepared. A phosphor film 43 of SiO₂+EuO is formed to athickness of 0.5 μm by magnetron sputtering, using the target. Thesubstrate temperature is varied from the room temperature to 1,000° C.during the sputtering process. Then, an insulating film is formed to athickness of 10 nm and subsequently a transparent electricallyconductive film 41 of ITO is formed to a thickness of 300 nm.

When the obtained film is observed through an electron microscope, it isfound that cylinders of EuO are formed in a dispersed state so as to besurrounded by an SiO₂ region. When the composition of the target ischanged to raise the ratio of the SiO₂ content, dispersed fine particlesof EuO are formed and surrounded by the SiO₂ region. The averagediameter of the cylinders or the fine particles of EuO is betweenseveral nanometers and hundreds of several nanometers, although itdepends on the film deposition conditions and the crystal is large andclear when the substrate temperature is high in the film depositionprocess.

When a DC voltage is applied between the transparent electrode film 41and the electrode film 45 so as to gradually raise the voltage, emissionof red light begins when the voltage gets to 20V. The emitted light isparticularly bright when the substrate temperature is not lower than400° C.

EXAMPLE 3

A light-emitting material of a V₂O₅—Y₂O₃ system is prepared in thisexample by using a technique similar to the one used in Example 1.

A quartz substrate is used as substrate in this example. An electrodefilm 45 is formed by depositing Ti and Pt to respective thicknesses of10 nm and 50 nm on a substrate 46 by magnetron sputtering. Subsequently,a dielectric film 44 is formed by depositing Ta₂O₅ to a thickness of 0.5μm also by magnetron sputtering. Thereafter, a phosphor film 43 isformed in a manner as described below.

A target with a composition showing a volume ratio of V₂O₅ to Y₂O₃:Euequal to 5 to 1 is prepared. A phosphor film 43 of V₂O₅+Y₂O₃:Eu isformed to a thickness of 1 μm by magnetron sputtering, using the target.The substrate temperature is varied from the room temperature to 1,000°C. during the sputtering process. Then, a dielectric film 42 of BaTiO₃is formed to a thickness of 2 μm and subsequently a transparentelectrically conductive film 41 of ITO is formed to a thickness of 300nm.

When the obtained film is observed through an electron microscope, it isfound that fine particles of Y₂O₃:Eu are formed in a dispersed state soas to be surrounded by a region of V₂O₅. The average diameter of thefine particles of Y₂O₃:Eu is between several nanometers and hundreds ofseveral nanometers, although it depends on the film forming conditionsand the crystal is large and clear when the substrate temperature ishigh in the film deposition process.

When an AC voltage of 1 KHz is applied between the transparent electrodefilm 41 and the electrode film 45 so as to gradually raise the voltage,emission of red light begins when the voltage gets to 150V. The emittedlight is particularly bright when the substrate temperature is not lowerthan 300° C.

EXAMPLE 4

In this example, as shown in FIG. 6, a light-emitting material accordingto the invention is used as a phosphor thin film for exciting electronbeams.

A transparent electrically conductive film 63 of SnO₂:F is formed to athickness of 300 nm on a glass substrate 64 and then NiO and Y₂O₃:Eu aredeposited thereon to form a film to a thickness of 2 μm by sputtering.NiO and Y₂O₃:Eu are made to show a ratio of 2:1 in order to form aphosphor film 62. Then, Al is deposited thereon to form an electrodefilm 61 to a thickness of 50 nm.

The prepared product is put into a vacuum chamber and irradiated withelectron beams to evaluate the phosphor. As a result, it is found thatit emits red light. As a result of comparing a known ordinary Y₂O₃:Euthin film and the phosphor thin film, the ordinary phosphor film with noelectrode film 61 is easily charged up, while the phosphor film of thepresent invention with no electrode film 61 is charged up only veryslightly.

EXAMPLE 5

In this example, a light-emitting element according to the invention isapplied to an image display apparatus, an illumination apparatus or aprinting apparatus.

An image display apparatus comprising light-emitting elements accordingto the invention can be used by linearly arranging the electrodes of thelight-emitting elements on the upper and lower surfaces, connecting themby matrix wiring and driving the light-emitting elements. To producecolor images, the colors of RGB can be generated by using RGB filters incombination with a light-emitting material adapted to emit white lightor by forming films of light-emitting materials that respectivelycorrespond to RGB and patterning them highly precisely. Alternatively,the colors of RGB can be generated by using a blue light-emittingmaterial and converting blue light into green light and red light bymeans of corresponding phosphors.

A technique of using white light-emitting material, that of laying RGBlight-emitting materials in a vertical direction or that of emittingblue rays of light or ultraviolet rays and converting them into RGB raysof light may be employed when a light-emitting element according to theinvention is applied to an illumination apparatus.

When a light-emitting element according to the invention is employed todisplay images, a plurality of pixel sections can be formed by dividingat least the upper side electrode or the lower side electrode into aplurality of electrodes.

When a light-emitting element according to the invention is applied to aprinting apparatus, or a printer, it is possible to linearly arrangelight-emitting elements and drive them instead of scanning a laser beamby means of a polygon mirror.

EXAMPLE 6

In this example, the diameter of each of the cylinders in a phosphorfilm according to the invention is made to change continuously and showpointed apexes as shown in FIG. 7 so that a concentrated high electricfield may appear at the light-emitting sections when the phosphor filmis used to operate as EL element.

A quartz substrate is used for the substrate 46 as shown in FIG. 8. Anelectrode film 45 is formed by depositing Ti and Pt to respectivethicknesses of 10 nm and 100 nm on a substrate 46 by magnetronsputtering. Subsequently, a dielectric film 44 is formed by depositingTa₂O₅ to a thickness of 0.5 μm also by magnetron sputtering. Thereafter,a phosphor film 43 is formed in a manner as described below.

Two targets of ZnO and WO₃ are used to prepare a phosphor film 43containing cylinders with pointed apexes formed at the opposite ends bymagnetron sputtering, following the sequence as described below.

Firstly, the two targets of ZnO and WO₃ are made to produce electricdischarges of RF400W and RF600W respectively. The two shutters areclosed at the beginning. Then, the shutter at the side of the ZnO isopened for film forming for one minute and subsequently the shutter atthe side of the WO₃ is opened to start forming a eutectic film ofZnO—WO₃. Then, the total applied power is continuously reduced to 100 Win 20 minutes, maintaining the ratio of the applied powers of the twotargets.

When the total applied power gets to 100 W, the film growth rate ismaintained for 40 minutes and, subsequently, the total applied power israised to 1 kW in 20 minutes. Finally, the shutter at the side of theWO₃ is closed and the operation of forming the ZnO film is continued forone minute to produce a phosphor film with a total film thickness of 1μm. During the phosphor film forming process, the substrate temperatureis varied from room temperature to 1,000° C. Thereafter, a BaTiO₃ filmis formed to a thickness of 2 μm as dielectric film 42. Subsequently, anITO film is formed as transparent electrically conductive film 41 to athickness of 300 nm.

When the obtained film is observed through an electron microscope, it isfound that dispersed fine pieces of WO₃ having pointed apexes andsurrounded by a ZnO region are produced. The film forming rate falls asthe applied power is reduced. Then, it is possible to raise the surfacemigration length of sputtered particles on the film surface and thecylinder diameter by gradually reducing the deposition.

Thus, it is possible to prepare nano-composite structures having variousdifferent profiles by forming films, controlling the diameter of thecylinders in this way. The average diameter of the cylinders is betweenseveral nanometers and hundreds of several nanometers, although itbecomes large and clear as the substrate temperature rises.

When an AC voltage of 1 KHz is applied between the transparent electrodefilm 41 and the electrode film 45 so as to gradually raise the voltage,emission of blue white light begins when the voltage gets to about 120V.The emitted light is particularly bright when the substrate temperatureis not lower than 400° C. during the film forming process. The luminanceis improved to more than twice if compared with a structure where theopposite ends of cylinders do not have pointed apexes nor are narrowed.

This application claims priority from Japanese Patent Application No.2004-092402 filed Mar. 26, 2004, and Japanese Patent Application No.2004-253253 filed Aug. 31, 2004 which are hereby incorporated byreference herein.

1. A light-emitting material including: a matrix section andlight-emitting sections dispersed and buried in the matrix section; thematrix section comprising a first material, the light-emitting sectionscomprising a second material showing a eutectic relationship with thefirst material.
 2. The light-emitting material according to claim 1,wherein said light-emitting sections are granular, or cylindrical. 3.The light-emitting material according to claim 1, wherein saidlight-emitting sections have pointed apexes.
 4. The light-emittingmaterial according to claim 1, wherein said first and second materialsare oxides.
 5. The light-emitting material according to claim 4, whereinsaid oxides are a combination of magnesium oxide and an oxide of a rareearth element, a combination of nickel oxide and an oxide of a rareearth element, a combination of vanadium oxide and a vanadium compositeoxide containing a rare earth element, a combination of silicon oxideand a silicon composite oxide containing a rare earth element or acombination of tungsten oxide or zinc oxide and a tungsten compositeoxide containing zinc.
 6. A light-emitting element comprising: alight-emitting layer and a pair of electrodes arranged so as to sandwichthe light-emitting layer; the light-emitting layer including a matrixsection and light-emitting sections dispersed and buried in the matrixsection; the matrix section comprising a first material, thelight-emitting sections comprising a second material showing a eutecticrelationship with the first material.
 7. The light-emitting elementaccording to claim 6, wherein said light-emitting layer has regionslocated near the opposite surfaces that are free from light-emittingsections.
 8. The light-emitting element according to claim 6, wherein adielectric film is arranged between said light-emitting layer and atleast one of said electrodes.
 9. An image display apparatus comprising alight-emitting element according to claim 6, at least one of theelectrodes of said light-emitting element being divided into a pluralityof electrodes.